In recent years, multilane and densification in optical transmission are progressed along with an increase in communication capacity between devices. Multilane and densification in optical transmission may be realized by narrowing an interval between channels, for example.
However, when the interval between channels is narrowed, crosstalk easily occurs. For example, when an optical axis deviation occurs between a vertical cavity surface emitting laser (VCSEL) array which is included in a transmission module and a lens block, light beams output from the VCSEL are not only input to a predetermined lens (regular lens), but also are leaked to a portion between the regular lens and a lens adjacent thereto (adjacent lens), or are input to the adjacent lens. The light beams which are input to the regular lens are guided to a predetermined optical fiber (regular optical fiber); however, there is a case in which the light beams leaked to a portion between the regular lens and the adjacent lens, and the light beams input to the adjacent lens are guided to an optical fiber adjacent to the regular optical fiber (adjacent optical fiber). An occurrence of crosstalk leads to a deterioration in transmission quality.
Accordingly, in order to suppress an occurrence of crosstalk, an improvement in manufacturing accuracy of a component itself which is used in optical transmission and an improvement in a positioning accuracy between components have been attempted.
However, it is desirable to use an expensive manufacturing device in order to improve the manufacturing accuracy, and it takes time for adjusting in order to improve the positioning accuracy. That is, in the related art, it is difficult to obtain a highly effective and excellent transmission quality.
The followings are reference documents.    [Document 1] Japanese Laid-open Patent Publication No. 11-289317 and    [Document 2] Japanese Laid-open Patent Publication No. 2005-242331.